In LaTeX, font selection is usually done through NFSS mechanism, and mathematical fonts are no exception. The basic command to switch to mathematical bold is \boldmath, which is usually defined as \mathversion{bold}, which means that the current mathematical font is set to bold globally and should be used outside the mathematical environment. The relative thickness to return to normal is \ unbold path \ mathversion {normal}. Similar to amsbsy, it is more powerful and specializes in dealing with bm macro packets in blackbody mathematics. The main command provided by the bm macro package is \bm, which, like the \ bold symbol of amsmath, outputs the mathematical symbols in the parameters in bold. The difference is that when a bold font is available for the symbol, its function is roughly the same as that of \boldsymbol, and the corresponding bold output will be selected; When the symbol has no available bold font, its function is the same as that of \pmb, and it will be output in pseudo bold. In addition, bm macro package is more detailed than amsbsy in parameter nesting and mathematical letter font switching.